Of all the damning phrases connected with the Bush administration, one stands out in the memory – "reality-based community". Karl Rove's reported dismissal of those who insisted on anchoring their beliefs in something as mundane as the facts was a line to lure sensible Britons into feeling smug. Politics might be lacklustre in the UK, runs the thought, but at least it retains some rationality.

Don't bank on it. We are amid an election campaign dominated by Ukip billboards screaming about 26 million Europeans who are after your job. And Westminster was not yesterday in a mood to trouble itself with the actuality, when official statistics revealed that the number of Romanians and Bulgarians working in Britain has not risen but fallen since immigration restrictions were eased amid a bout of hysteria at the end of last year.

Every aspect of the data pointed to Nigel Farage and his media cheerleaders having whipped up fears that had not come to pass. There are still only 122,000 Romanians and Bulgarians in the labour force, whereas anti-immigration campaigners had predicted that 250,000 extra souls would arrive over the next several years. A high and rising employment rate for the group of around 75% gives the lie to talk of an influx of benefits tourism. And the overwhelming majority of the new jobs created over the last year have gone not to foreigners but to British nationals.

So where were the mainstream politicians on Wednesday, coming forward to shoot Ukip down with the facts? In the Commons, David Cameron described the data merely as "notable", a formulation designed to discourage headlines. Theresa May kept her head down, the Home Office making no statement at all. For Labour, Yvette Cooper at least acknowledged "shrill" predictions had not come to pass, but continued to stress "legitimate concerns" too. It is almost as if the big parties had given up on any hope of making a "reality-based" appeal.

There is a cynical aspect to the decision to shrink from the fight, a straightforward partisan calculation for both government and opposition. Noting that they are reliably more trusted than Labour on immigration, the Tories have no interest in reducing the issue's salience. Meanwhile Labour, itself newly pressed in the polls, clings to the thought that all politics is relative, and the hope that Ukip can mop up enough Tory votes to pull the Conservatives below Labour in the Euro stakes.

There is, however, a deeper reason why both front benches are reluctant to thrash Ukip back with the facts: they doubt they would be believed. Xenophobia, or something close to it, is one factor here – the stubborn belief on the part of a smallish minority of voters that the country is going to the dogs thanks to an influx of outsiders. This is not, however, the chief reason why Westminster shrinks from explaining to the country that immigration is not the disaster for Britain that Ukip pretends. The wider problem is ubiquitous distrust of the governed towards the governing classes, and indeed a yawning disconnection between the two. The politicians feel, and they may be right, that the country is simply not in a mood to be lectured by them about anything.

Aside from immigration, Wednesday's labour market data also included the latest instalment in a slow saga of sluggish wage rises, a story that has now involved day-to-day life getting tougher across the bulk of the country over six successive years. Even before the downturn, desiccated political parties were finding it hard to make themselves heard. In its aftermath, amid stubborn economic insecurity, there are communities which recall rapid bouts of immigration a few years ago as one more thing that disrupted life.

Any politician taking on Ukip's slogans with statistics fears that – to a hard-up, hard-pressed listener with only half an ear on the radio – their words could come across as a diatribe of denial. The temptation to sit quiet is understandable, but it must be resisted. For before politics can do anything useful at all, it must first face the facts.